GaN Whiskers and Methods of Growing Them from Solution

ABSTRACT

Millimeter-scale GaN single crystals in filamentary form, also known as GaN whiskers, grown from solution and a process for preparing the same at moderate temperatures and near atmospheric pressures are provided. GaN whiskers can be grown from a GaN source in a reaction vessel subjected to a temperature gradient at nitrogen pressure. The GaN source can be formed in situ as part of an exchange reaction or can be preexisting GaN material. The GaN source is dissolved in a solvent and precipitates out of the solution as millimeter-scale single crystal filaments as a result of the applied temperature gradient.

CROSS-REFERENCE

This application claims the benefit of priority based on U.S.Provisional Patent Application No. 61/623,420 filed on Nov. 23, 2009,the entirety of which is hereby incorporated by reference into thepresent application.

TECHNICAL FIELD

The present invention relates to millimeter-scale single crystal galliumnitride (GaN) filaments, also known as GaN whiskers, and methods ofgrowing such whiskers from solution.

BACKGROUND

Nitrides of indium (In), gallium (Ga), and aluminum (Al) and compoundsthereof have many applications, including high-power and light-emittingdevices. By moving to one dimensional, i.e. nanoscale, materials, a hostof new applications become available.

Current nanoscale GaN technology is based on nanowires grown either bymetal organic chemical vapor deposition (MOCVD) or molecular beamepitaxy (MBE). These nanoscale materials are defined by having verylarge surface to volume ratios. When reducing the material to thisscale, surface effects can begin to dominate the material properties anddegrade performance. For example, in optical applications, the largesurface area can cause photon scattering, while the small size alsorestricts the charge carrying capacity of the material.

One method for solving these problems involves using GaN material on amacro-scale, in the form of millimeter-scale filaments, also known aswhiskers. Such whiskers may bridge the gap between bulk and nanoscaleGaN. In this case, the material is more representative of the bulk, cancarry larger charges, and should show less phonon scattering. Inaddition, due to their larger size, the whiskers are easier tomanipulate. Growing the whiskers from solution also avoids the residualmetal catalysis beads found at the tip of nanowires and allows forcrystalline perfection.

SUMMARY

This summary is intended to introduce, in simplified form, a selectionof concepts that are further described in the Detailed Description. Thissummary is not intended to identify key or essential features of theclaimed subject matter, nor is it intended to be used as an aid indetermining the scope of the claimed subject matter. Instead, it ismerely presented as a brief overview of the subject matter described andclaimed herein.

The present invention provides millimeter-scale GaN single crystals infilamentary form, also known as GaN whiskers, grown from solution.

The present invention also provides a process that can be used to growsuch GaN whiskers at moderate temperatures and near atmosphericpressures.

In accordance with the present invention, GaN whiskers can be grown,either with or without a seed, from a solution in a reaction vesselsubjected to a temperature gradient at nitrogen pressure.

In a first exemplary embodiment of the present invention, a GaNfeedstock can be created in an initial reaction step which also createsa solvent for the GaN. The reaction vessel containing the formed GaNfeedstock and the formed solvent is subjected to a temperature gradientat constant pressure, wherein the GaN feedstock is dissolved in thesolvent in a region of the reaction vessel at or near the high end ofthe temperature gradient and precipitates, either self-seeded or on aseed, as GaN whiskers in a region of the reaction vessel at or near thelow end of the temperature gradient.

In a second exemplary embodiment of the present invention, the initialreaction step can be omitted, and a preexisting solid GaN sample can beplaced in a preexisting solvent in the reaction vessel. The reactionvessel can then be subjected to a temperature gradient at constantpressure, wherein the GaN feedstock is dissolved in the solvent in aregion of the reaction vessel at or near the high end of the temperaturegradient and precipitates, either self-seeded or on a seed, as GaNwhiskers in a region of the reaction vessel at or near the low end ofthe temperature gradient.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B are schematic cross-sectional views showing an exemplaryGaN growth reactor in accordance with the present invention. FIG. 1Aillustrates an exemplary initial configuration of the reactor before anexchange reaction which forms a GaN feedstock in accordance with a firstembodiment of the present invention. FIG. 1B illustrates the reactorcontaining a GaN feedstock dissolved in a solvent, where the GaNfeedstock is either one formed during the exchange reaction inaccordance with a first embodiment or a preexisting GaN feedstock inaccordance with a second embodiment of the present invention.

FIGS. 2A and 2B are schematic cross-sectional views showing an exemplaryGaN growth reactor which contains a GaN seed in accordance with furtherembodiments of the present invention. FIG. 2A illustrates an exemplaryinitial configuration of the reactor before an exchange reaction whichforms a GaN feedstock. FIG. 2B illustrates the reactor containing a GaNfeedstock dissolved in a solvent, where the GaN feedstock is either oneformed during the exchange reaction in accordance with a firstembodiment or a preexisting GaN feedstock in accordance with a secondembodiment of the present invention.

FIGS. 3A and 3B are optical images of exemplary GaN whiskers inaccordance with the present invention. FIG. 3A depicts an array of GaNwhiskers grown on a seed surface in accordance with the presentinvention. FIG. 3B depicts a single exemplary 2 mm long GaN whisker inaccordance with the present invention and illustrates its length andgrowth direction.

FIG. 4 is a room temperature micro-Raman spectrum of an exemplary GaNwhisker in accordance with the present invention.

FIGS. 5A-5C are optical images illustrating the flexibility andelasticity of an exemplary GaN whisker in accordance with the presentinvention.

DETAILED DESCRIPTION

The aspects and features of the present invention summarized above canbe embodied in various forms. The following description shows, by way ofillustration, combinations and configurations in which the aspects andfeatures can be put into practice. It is understood that the describedaspects, features, and/or embodiments are merely examples, and that oneskilled in the art may utilize other aspects, features, and/orembodiments or make structural and functional modifications withoutdeparting from the scope of the present disclosure.

The present invention provides millimeter-scale gallium nitride (GaN)single crystals in filamentary form, also known as GaN whiskers, grownfrom solution.

The present invention also provides a method that can be used to growGaN whiskers at moderate temperatures and near atmospheric pressures.

In accordance with the present invention, a GaN feedstock or othersource of GaN is dissolved in a reaction chamber at nitrogen pressure. Atemperature gradient is then applied to the reaction chamber. Thetemperature gradient and applied pressure control the dissolution of GaNin the solvent and cause GaN whiskers to precipitate from the solution.

In some embodiments, a seed crystal may be present in the reactionchamber. In such embodiments, the seed crystal is typically the coldestspot in the reaction vessel within the reactor when precipitation of GaNwhiskers takes place. Due to the driving force imparted to the GaNdissolved in the solvent, GaN leaves the solvent when the solventbecomes supersaturated with GaN and precipitates on the seed crystal aswhiskers and, if supersaturation is high enough, whiskers also nucleateand grow around the seed. In other embodiments, the process is carriedout without the seed crystal, and in such cases nucleation and growth ofGaN whiskers take place within the colder parts of the reaction vesselcontaining the solvent.

A first exemplary embodiment of the invention includes the formation ofa GaN feedstock and a solvent for the GaN during a first stage of thegrowth run in a self-developing process. Thus, in this embodiment, in afirst stage of a GaN whisker growth run, a GaN feedstock is formed by anexchange reaction of a Group IA and/or Group HA element (i.e., alkalimetal and/or alkaline earth metal) nitride with gallium in one part ofthe reaction chamber, while a solvent for the GaN simultaneously isformed in another part of the vessel. A detailed description of thisaspect of a process for growing millimeter-scale GaN whiskers inaccordance with the present invention is given in United States PatentApplication Publication No. 2009/0223440, which shares an inventor incommon with the present application and is hereby incorporated byreference into the present disclosure in its entirety.

This first exemplary embodiment of a process for growing single crystalGaN in accordance with the present invention is now described withrespect to the reaction apparatus shown in FIGS. 1A and 1B. FIG. 1Aillustrates an exemplary initial configuration of the growth reactor ina first embodiment of the present invention. As illustrated in FIG. 1A,a nitride layer 14 comprising a layer of a Group IA or/and Group IIAelement nitride is placed at the bottom of a reaction vessel 13 and ametallic layer 15 comprising a mixture of gallium with bismuth (Bi)or/and antimony (Sb) is disposed over the nitride layer 14. An alkalimetal, an alkaline earth metal, or any combination thereof may be addedto the metallic layer 15. Of the alkali metal nitrides, lithium nitrideis preferred, though other alkali metal nitrides and alkaline earthmetal nitrides may also be used, and all such embodiments are within thescope of the present disclosure.

The reaction vessel 13 with the thus-assembled charge is placed in anitrogen-filled reactor 10 which also contains a furnace 12 and has anitrogen inlet 11 at the top thereof. In a first step of a method forpreparing GaN whiskers in accordance with the present invention, thereaction vessel 13 and the charge therein are simultaneously subjectedto temperature and nitrogen pressure, both of which are in theGaN-stable region of the phase diagram of GaN. The nitrogen pressure issupplied via nitrogen introduced into the reaction vessel from inlet 11.During the growth run the pressure is maintained, for example, in arange of from about 0.1 MPa to about 20 MPa, though pressures outsidethis range may be appropriate as conditions warrant.

The reaction vessel 13 and charge are heated by means of furnace 12 to atemperature at which the Group IA/IIA element nitride in nitride layer14 reacts with the gallium in metallic layer 15. As a result of thisreaction, part of the Group IA and/or Group HA element is released fromcharge 14 and the released Group IA/IIA element is replaced by part ofthe gallium from metallic layer 15, with the result being the formationof GaN feedstock 18 shown in FIG. 1B. Simultaneously, the Group IAand/or Group IIA element released from charge 14 mixes with the residualgallium and other components in metallic layer 15 to form a moltensolvent 19 for the GaN. Thus, as a result of this first step inaccordance with this embodiment of the present invention, as illustratedin FIG. 1B, the reaction vessel 13 now contains a GaN feedstock 18 whichis covered by a layer of molten solvent 19.

In a second step of a method for preparing GaN whiskers in accordancewith this embodiment of the present invention, the reaction vessel 13 isheated by furnace 12 to a growth temperature which is higher thantemperature of the exchange reaction in the first step so that thesolvent remains in a molten state, but which is lower than thetemperature of GaN decomposition at the applied nitrogen pressure.

In addition, in accordance with the present invention, a temperaturegradient is maintained between the GaN feedstock 18 and the GaNdeposition site, whereby the temperature of solvent 19 which is near theGaN feedstock 18 is higher than the temperature of the solvent 19 whichis near the deposition site for the growth of the GaN whiskers. As aresult, the GaN feedstock 18 is dissolved in the relatively hotter partof solvent 19, creating a supersaturated solution of GaN in therelatively cooler part. The dissolved GaN then precipitates from thissupersaturated solution in the part of reaction vessel 14, which is atthe low end of the temperature gradient. In accordance with the presentinvention, the precipitated GaN is in the form of micro-scale single GaNcrystals in filamentary form, i.e., GaN whiskers.

In some embodiments, one or more GaN seed crystals 17, each held in acorresponding seed holder 16, may be immersed in or in contact with thesolvent 19, and in such cases the precipitated GaN can grow on the seed,while in other embodiments where such a seed crystal is not present, theGaN whiskers can grow after spontaneous nucleation inside the solution19. In either case, the GaN whiskers in accordance with the processdescribed above are micro-scale, growing up to several millimeters inlength.

A second exemplary embodiment of the process for producing GaN whiskersin accordance with the present invention can also be described withrespect to the illustrative reaction configuration shown in FIG. 1B.

This second exemplary embodiment of a process for growing GaN whiskersin accordance with the present invention uses a preexisting solid GaNsource prepared by HVPE GaN growth or any other suitable process as aGaN feedstock instead of the GaN feedstock formed from the Group IA/IIAnitride reacted with gallium as described above with respect to thefirst embodiment. As described in more detail below, when heated, thesolid GaN feedstock dissolves in a solvent comprising gallium with aGroup IA metal, a Group IIA metal, Bi, Sb, or any combination thereof,with lithium being a preferred Group IA/IIA metal, and the dissolved GaNis precipitated into single crystal whiskers.

Thus, in accordance with this embodiment of the present invention, acharge comprising a preexisting GaN feedstock 18 and a layer 19 ofsolvent is placed in reaction vessel 13 and the thus-filled reactionvessel 13 is placed into reactor 10 and heated under pressure asdescribed above with respect to the first exemplary embodiment. As inthe first embodiment, the reaction vessel 13 and charge aresimultaneously subjected to both temperature and pressure in theGaN-stable region of the phase diagram of GaN, where the vessel isheated to a liquefaction temperature of the solvent. A temperaturegradient is then provided by furnace 12, wherein one part of thereaction vessel is maintained at a higher temperature than another part,and in accordance with the present invention, the GaN feedstock 18dissolves in solvent 19 within the part of reaction vessel 13 at thehigh end of the temperature gradient and precipitates out of thesolution as GaN whiskers in the part of reaction vessel 14 which is atthe low end of the temperature gradient. As in the first embodimentdescribed above, the whiskers can be self-seeded, growing insidesolution 19, or can be grown on a seed 17 if one or more is presentwithin the cooler part of the reaction vessel, and in either case, canbe up to several millimeters in length.

In some embodiments a GaN seed can be placed at the bottom of thereaction vessel. These embodiments are illustrated in FIGS. 2A and 2B,where the numbered elements correspond to the numbered elements shown inFIGS. 1A and 1B with the substitution of the numeral “2” for the numeral“1”, e.g., reaction vessel 13 shown in FIG. 1A becomes reaction vessel23 shown in FIG. 2A.

Thus, as shown in FIG. 2A, in an additional embodiment of the invention,a GaN seed 27 can be placed at the bottom of the reaction vessel 23. TheGaN seed 27 can then be covered with a metallic layer 25 comprising amixture of gallium with Bi, Sb, a Group IA element, a Group IIA element,or any combination thereof, with a nitride layer 24 comprising a solidGroup IA and/or Group IIA element nitride disposed on top of metalliclayer 25. In other words, the layer order in this embodiment is reversedfrom the order described above with respect to FIG. 1A.

The reaction vessel 23 containing the thus-assembled charge can then beplaced in reactor 20 with nitrogen source 21 and furnace 22, be heatedunder nitrogen pressure to induce an exchange reaction to form a GaNsource and a solvent as described with respect to the first embodimentabove, and subsequently be subjected to a temperature gradient thatcauses the dissolved GaN to precipitate as GaN whiskers in the coolerpart of the solvent. However, in this embodiment, rather than formingbelow the solvent as in the first embodiment, as shown in FIG. 2B, theGaN source 28 is formed at the top of the charge located within thereaction vessel, with the solvent 29 being formed under the source. Inaddition, in this embodiment, the temperature gradient applied byfurnace 22 is in the opposite direction from that applied in the firstembodiment described above, so that the GaN whiskers are formed on seed27 at the bottom of the reaction chamber 23.

In another embodiment, corresponding to the second exemplary embodimentdescribed above and also illustrated in FIG. 2B, seed 27 can be placedat the bottom of reaction vessel 23 and be covered with a solvent layer29 comprising gallium with Bi, Sb, a Group IA element, a Group IIAelement, or any combination thereof, which in turn is covered by a solidGaN source 28. Again, it should be noted that the layer structure inthis embodiment and as shown in FIG. 2B is the opposite of the layerstructure described above with respect to FIG. 1B.

As with the second embodiment described above, the reaction vessel 23and charge are simultaneously subjected to both temperature and pressurein the GaN-stable region of the phase diagram of GaN whereby solvent 29becomes a molten solvent which dissolves the solid GaN 26 therein, withthe thus-dissolved GaN precipitating as single-crystal GaN whiskers uponthe application of a temperature gradient. In this case, however, theapplied temperature gradient is in the opposite direction from thatapplied in the second embodiment, and thus in this embodiment the GaNwhiskers precipitate onto seed 27 at the bottom of the reaction vessel.

In all of these cases, during the process of GaN growth, the pressuresand temperatures used can be in a moderate range and thus can be readilyaccomplished using easily available equipment. For example, the solventreaches a molten state when the reaction vessel is heated to atemperature in the range of 700-900° C., more typically 750-850° C., andthe nitrogen pressure in the growth reactor is typically aboveatmospheric, more typically 0.1-2.0 MPa. The temperature gradient, i.e.,the temperature difference inside the solvent between the GaN source andthe growing crystal, is typically 1-100° C. across the thickness of thesolvent, and more typically 5-50° C.

Having described various exemplary embodiments of the invention, thefollowing examples are given as further particular embodiments thereofand to demonstrate the practice and advantages thereof. It is understoodthat the examples are given only by way of illustration and are notintended to limit the scope of the claims in any manner.

Example 1

This example demonstrates preparation of GaN whiskers at moderatetemperature and moderate pressure in accordance with the presentinvention using a charge comprising lithium nitride, gallium andbismuth. All material preparations of the charge were carried out insidea glove box under a nitrogen atmosphere with moisture and oxygen contentbelow 1 ppm.

In this example, a layer of commercially available lithium nitride whichhad been previously compacted into a pill of approximately 1.2 g wasplaced at the bottom of the reaction vessel. A mixture of 15.0 g ofgallium and 0.5 g of bismuth was then placed in a layer on top of thelithium nitride pill.

After the reaction vessel was filled with the charge, it was placed intothe reactor. The reactor was evacuated to a vacuum level of 10⁻³ Torr,filled with nitrogen of 99.999% purity to a pressure of 0.1 MPa and thenevacuated to a vacuum level of 10⁻³ Torr once more. After theevacuation, the furnace was filled with nitrogen of 99.999% purity to apressure of 0.24 MPa.

The reaction vessel was then heated by a furnace. During heating, partof the gallium reacted with the lithium nitride in an exchange reactionto form a gallium nitride source at the bottom of the crucible. At thesame time, the lithium released during the exchange reaction mixed withresidual liquid gallium and formed a solvent for gallium nitride on topof the gallium nitride source.

After the completion of the exchange reaction, the reaction vessel wasfurther heated so that the temperature at the lower end of the reactionvessel, where the gallium nitride source was located, was maintained at800° C., while the temperature at the higher end, where the solvent waslocated, was maintained at 790° C., resulting in a temperaturedifference of 10° C. from the bottom of the solvent layer to its top inthe reaction vessel. Gallium nitride source started to dissolve in thecreated solvent, saturating the solution. A piece of polycrystallinegallium nitride seed was immersed from the top into the solution whenthe temperature at the bottom reached 800° C. The growth conditions ofthe process were maintained for 54 hours, following which thepolycrystalline seed was pulled out, the reactor was cooled to roomtemperature, and the nitrogen pressure was allowed to be reduced toatmospheric.

After cleaning the remaining solution from the seed, the grown GaNwhiskers shown in FIG. 3A were found on the immersed portion of the seedand also inside the top layer of the solution around the seed. Asillustrated in FIG. 3B, the whiskers grew in the c-direction, with someof the whiskers being up to 2 mm long. Micro-Raman measurementsillustrated in FIG. 4 confirmed that the whiskers were single crystalGaN with structural quality and low impurity concentration.

In addition, the grown single crystal GaN whiskers exhibited exceptionalmechanical properties. As illustrated in FIGS. 5A, 5B, and 5C, theycould be bent without breaking and elastically returned to their initialstraight shape.

Example 2

This example demonstrates preparation of GaN whiskers at moderatetemperature and moderate pressure in accordance with the presentinvention, using a charge comprising a preexisting GaN source and amixture of gallium, antimony, and bismuth.

A piece of commercially available polycrystalline GaN of approximately0.8 g was placed at the bottom of the reaction vessel (crucible). Amixture of a mixture of 8.0 g of gallium, 0.1 g of Sb and 0.150 g of Biwas placed on top of the GaN source to complete the charge.

After the reaction vessel was filled with the charge, it was placed intothe reactor. The reactor was evacuated to a vacuum level of 10⁻³ Torr,filled with nitrogen of 99.999% purity to a pressure of 0.1 MPa and thenevacuated to a vacuum level of 10⁻³ Torr once more. After theevacuation, the furnace was filled with nitrogen of 99.999% purity to apressure of 0.25 MPa.

The reaction vessel was then heated by the furnace such that thetemperature of the lower end of the reaction vessel was maintained at800° C. and the temperature at the higher end of the solvent wasmaintained at 790° C., thereby resulting in a temperature difference of10° C. inside the solvent in the reaction vessel. Gallium nitride sourcestarted to dissolve in the created solvent, saturating the solution. Aseed of polycrystalline HVPE gallium nitride was partly immersed fromthe top into the solution when the temperature at the bottom reached800° C. The growth conditions of the process were maintained for 62hours. At the end of that time period, the seed was pulled out, thesystem was cooled to room temperature, and the nitrogen pressure wasallowed to be reduced to atmospheric. After cleaning the remainingsolution from the seed, grown GaN whiskers were found on the immersedportion of the seed and also inside the top layer of the solution aroundthe seed. These whiskers exhibited similar characteristics as thosedescribed above with respect to the whiskers grown in Example 1.

Thus, as described herein, in accordance with the present invention,micro-scale GaN whiskers readily can be grown from solution at moderatetemperatures and pressures, using easily available equipment.

Although particular embodiments, aspects, and features have beendescribed and illustrated, it should be noted that the inventiondescribed herein is not limited to only those embodiments, aspects, andfeatures, and it should be readily appreciated that modifications may bemade by persons skilled in the art. The present application contemplatesany and all modifications within the spirit and scope of the underlyinginvention described and claimed herein, and all such embodiments arealso contemplated to be within the scope and spirit of the presentdisclosure.

1. A process for growing gallium nitride whiskers from solution,comprising: (a) charging a reaction vessel with a layer of one selectedfrom the group consisting of a Group IA element nitride, a Group IIAelement nitride, and combinations thereof; (b) adding a layer of galliummixed with at least one of bismuth and antimony, the gallium-basedmixture being in contact with the layer of the one selected from thegroup consisting of a Group IA element nitride, a Group IIA elementnitride, and combinations thereof; (c) placing the charged reactionvessel into a chamber; (d) applying pressure to the reaction vessel toprevent dissociation or decomposition of the one selected from the groupconsisting of a Group IA element nitride, a Group IIA element nitride,and combinations thereof and the gallium nitride; (e) forming in situ agallium nitride source by heating the charged reaction vessel to renderthe gallium reacted with the one selected from the group consisting of aGroup IA element nitride, a Group IIA element nitride, and combinationsthereof in an exchange reaction; (f) forming in situ a solventcomprising the gallium-based mixture and the one selected from the groupconsisting of a Group IA element, a Group IIA element, and combinationsthereof released from the one of the Group IA element nitride and theGroup IIA element nitride during the exchange reaction; (g) providing atemperature at which the gallium nitride from the formed gallium nitridesource dissolves in the formed solvent; and (h) providing a temperaturedifference in the solvent between a first region of the reaction vesseland a second region of the reaction vessel, the first region of thereaction vessel being at a relatively higher temperature than the secondregion of the reaction vessel; wherein the gallium nitride from theformed gallium nitride source dissolves in the formed solvent in thefirst region of the reaction vessel and precipitates out of the solutionas gallium nitride whiskers in the second region of the reaction vessel.2. The process of claim 1, wherein the charged reaction vessel is heatedto a liquefaction temperature of the solvent.
 3. The process of claim 1,wherein the temperature difference is about 1-100° C. across a depth ofthe solvent.
 4. The process of claim 1, wherein the charged reactionvessel is heated in an atmosphere comprising nitrogen gas at a pressureof about 0.1-20 MPa.
 5. The process of claim 1, wherein the chargedreaction vessel is heated in an atmosphere comprising nitrogen gas at apressure of about 0.2 MPa.
 6. The process of claim 5, wherein thegallium nitride whiskers are grown at temperature of about 700-900° C.7. The process of claim 5, wherein the gallium nitride whiskers aregrown at temperature of about 750-850° C.
 8. The process of claim 1,wherein the one selected from the group consisting of a Group IA elementnitride, a Group IIA element nitride, and combinations thereof islithium nitride.
 9. The process of claim 1, further comprising exposinga gallium nitride seed to the solvent, wherein the gallium nitrideprecipitates out of the solution as gallium nitride whiskers on theseed.
 10. The process of claim 9, wherein the gallium nitride seed isone selected from the group consisting of a single crystal galliumnitride, a polycrystalline gallium nitride, and a wafer of galliumnitride.
 11. The process of claim 1, wherein the gallium nitride sourcecomprises gallium nitride formed by the exchange reaction between thegallium and the one selected from the group consisting of a Group IAelement nitride, a Group IIA element nitride, and combinations thereofand further comprises gallium nitride added to the charge, the addedgallium nitride being in one of compacted and polycrystalline form. 12.The product of the process of claim
 1. 13. A process for growing galliumnitride whiskers from solution, comprising: (a) charging a reactionvessel with a layer of one selected from the group consisting of a GroupIA element nitride, a Group IIA element nitride, and combinationsthereof; (b) adding a layer of gallium mixed with at least one ofbismuth and antimony and at least one of a Group IA and a Group IIAelement, the gallium-based mixture being in contact with the layer ofthe one selected from the group consisting of a Group IA elementnitride, a Group IIA element nitride, and combinations thereof; (c)placing the charged reaction vessel into a chamber; (d) applyingpressure to the reaction vessel to prevent dissociation or decompositionof the one selected from the group consisting of a Group IA elementnitride, a Group IIA element nitride, and combinations thereof and thegallium nitride; (e) forming in situ a gallium nitride source by heatingthe charged reaction vessel to render the gallium reacted with the oneselected from the group consisting of a Group IA element nitride, aGroup IIA element nitride, and combinations thereof in an exchangereaction; (f) forming in situ a solvent comprising the gallium-basedmixture and the one selected from the group consisting of a Group IAelement, a Group IIA element, and combinations thereof released from theone of the Group IA element nitride and the Group IIA element nitrideduring the exchange reaction; (g) providing a temperature at which thegallium nitride from the formed gallium nitride source dissolves in theformed solvent; and (h) providing a temperature difference in thesolvent between a first region of the reaction vessel and a secondregion of the reaction vessel, the first region of the reaction vesselbeing at a relatively higher temperature than the second region of thereaction vessel; wherein the gallium nitride from the formed galliumnitride source dissolves in the formed solvent in the first region ofthe reaction vessel and precipitates out of the solution as galliumnitride whiskers in the second region of the reaction vessel.
 14. Theprocess of claim 13, wherein the heating is carried out to aliquefaction temperature of the solvent.
 15. The process of claim 13,wherein the temperature difference is about 1-100° C. across a depth ofthe solvent.
 16. The process of claim 13, wherein the charged reactionvessel is heated in an atmosphere comprising nitrogen gas at a pressureof about 0.1-20 MPa.
 17. The process of claim 13, wherein the chargedreaction vessel is heated in an atmosphere comprising nitrogen gas at apressure of about 0.2 MPa.
 18. The process of claim 17, wherein thegallium nitride whiskers are grown at temperature of about 700-900° C.19. The process of claim 17, wherein the gallium nitride whiskers aregrown at temperature of about 750-850° C.
 20. The process of claim 13,wherein the one selected from the group consisting of a Group IA elementnitride, a Group IIA element nitride, and combinations thereof islithium nitride.
 21. The process of claim 13, further comprisingexposing a gallium nitride seed to the solvent, wherein the galliumnitride precipitates out of the solution as gallium nitride whiskersprecipitates on the seed.
 22. The process of claim 21, wherein thegallium nitride seed is one selected from the group consisting of asingle crystal gallium nitride, a polycrystalline gallium nitride, and awafer of gallium nitride.
 23. The process of claim 13, wherein thegallium nitride source comprises gallium nitride formed by the exchangereaction between the gallium and the one selected from the groupconsisting of a Group IA element nitride, a Group IIA element nitride,and combinations thereof and further comprises gallium nitride added tothe charge, the added gallium nitride being in one of compacted andpolycrystalline form.
 24. The product of the process of claim
 13. 25. Aprocess for growing gallium nitride whiskers from solution, comprising:(a) charging a reaction vessel with a gallium nitride source; (b) addinga solvent to the reaction vessel, the solvent comprising gallium mixedwith one selected from the group consisting of a Group IA element, aGroup IIA element, and combinations thereof and bismuth, antimony, andcombinations thereof, the solvent being in contact with the galliumnitride source; (c) placing the charged reaction vessel into a chamber;(d) applying pressure to the reaction vessel to prevent dissociation ordecomposition of the gallium nitride; (e) providing a temperature atwhich the gallium nitride from the gallium nitride source dissolves inthe solvent; and (f) providing a temperature difference in the solventbetween a first region of the reaction vessel and a second region of thereaction vessel, the first region of the reaction vessel being at arelatively higher temperature than the second region of the reactionvessel; wherein the gallium nitride from the gallium nitride sourcedissolves in the solvent in the first region of the reaction vessel andprecipitates out of the solution as gallium nitride whiskers in thesecond region of the reaction vessel.
 26. The process of claim 25,wherein the gallium nitride source comprises at least one of apolycrystalline gallium nitride, single crystal gallium nitride, andcompacted gallium nitride.
 27. The process of claim 25, wherein thecharged reaction vessel is heated to a liquefaction temperature of thesolvent.
 28. The process of claim 25, wherein the temperature differenceis about 1-100° C. across the solvent thickness.
 29. The process ofclaim 25, wherein the charged reaction vessel is heated in an atmospherecomprising nitrogen gas at a pressure of about 0.1-20 MPa.
 30. Theprocess of claim 25, wherein the charged reaction vessel is heated in anatmosphere comprising nitrogen gas at a pressure of about 0.2 MPa. 31.The process of claim 29, wherein the gallium nitride whiskers are grownat temperature of about 700-900° C.
 32. The process of claim 31, whereinthe gallium nitride whiskers are grown at temperature of about 750-850°C.
 33. The process of claim 25, wherein the one selected from the groupconsisting of a Group IA element, a Group IIA element, and combinationsthereof is lithium.
 34. The process of claim 25, wherein the oneselected from the group consisting of a Group IA element and a Group IIAelement is lithium, and further wherein the combinations thereof islithium with at least one of another Group IA element and a Group IIAelement.
 35. The process of claim 25, further comprising exposing agallium nitride seed to the solvent, wherein the gallium nitrideprecipitates out of the solution as gallium nitride whiskers on theseed.
 36. The process of claim 35, wherein the gallium nitride seed isone selected from the group consisting of a single crystal galliumnitride, a polycrystalline gallium nitride, and a wafer of galliumnitride.
 37. The product of the process of claim 25.